Development of high power gyrotrons at 110 GHz and 140 GHz

High-power, long-pulse or CW millimeter-wave sources are required in electron cyclotron heating or current drive for fusion experiments. Gyrotron oscillators have served as effective sources in this area for many years. To reduce system cost, megawatt gyrotrons are required. At CPI, various programs are underway to deliver long pulse or CW megawatt gyrotrons. In particular, we are building a 110 GHz, 10 sec, 1.5 MW gyrotron. This gyrotron will be completed in early 2004. In addition, we have fabricated and are currently testing a 1 MW CW gyrotron at 140 GHz. Key features of these two gyrotrons include quasi-optical internal converters, diode-type electron guns, CVD (chemical vapor deposition) diamond output windows, and single-stage depressed collectors. In this paper, we will summarize the basic design of the 110 GHz and 140 GHz gyrotrons and report on the experimental results obtained on the megawatt, CW, 140 GHz gyrotron.